ranged from 272 to 340 mm . Only one 5 has 

 been caught, and it measured 289 mm . Appen- 

 dix tables 6-10 give the number of bluebacks of 

 each age in each 10-mm. interval. 



The lengths of each age group in the 

 preceding paragraphs include the extremes of 

 the 1949 53 data; thus the range of the lengths 

 is extended by any differences in growth that 

 exist between the years. Figure 18 shows the 

 maximum, minimum, and average lengths of 

 each age group, with 95 percent confidence 

 limits of the ranges and means. The 2's tend 

 to be skewed more than the other ages, possib- 

 ly indicating that the growth rate of bluebacks 

 in fresh water is greatest during the summer of 

 the second year. Large 2's measuring over 

 200 mm . are caugjit in the fall at Bonneville . 



Estimating Ages from Lengths 



Foerster (1929) observed that the pre- 

 diction of ages from lengths looked promising 

 for Cultus Lake socKeye (O. nerka) migrants. 

 Estimating ages of Columbia River bluebacks 

 is more difficult. The Cultus Lake fish are of 

 a single population that migrates within a short 

 period in the spring, whereas the Columbia 

 River population is mixed and migrates through- 

 out the year. 



Time of migration and lengths of age 

 groups have been discussed. Most of the down- 

 stream-migrant blueback can be separated by 

 using these data . Complete separation of the 

 age groups is simpler if the year is divided at 

 week 25 (June 18). Before week 25, scales 

 should be read for lengths 84 mm . and less to 

 separate the I's and 2's, for lengths between 

 160 and 200 mm. to separate the 2's and 3's, 

 and for all those over 280 mm. to separate the 

 3's, 4's, and 5's. Spring hatchery releases 

 contribute fish that are larger than the wild 

 migrants, and extend the maximum lengths for 

 the I's and 2's before week 25. After week 24, 

 scales should be read for fish 120 mm. and 

 less to separate the Is and 2's, and for all 

 over 190 mm. to separate the 2's and 3's. 



MIGRATION OF MARKED HATCHERY - 

 REARED FISH 



Rate of Travel of Marked Fish 



All of the information on rate of travel 

 used in this report comes from the catches of 

 marked fish which were released from hatcher- 

 ies above Bonneville. It is realized that these 

 marked fish may differ in rate of migration 

 from the unmarked and wild fish. Although it 

 is difficult to draw conclusions, apparently fish 

 released in the fall do not migrate until the fol- 

 lowing spring, whereas the spring-released 

 fish migrate immediately, but not as a single 

 school . 



The fastest and slowest moving fish 

 came from the same lot of 25, 000 I's, marked 

 adipose, which were released at Winthrop on 

 April 18, 1951 . On April 26, one of these fish 

 was caught at Bonneville; this fish averaged a 

 little over 50 miles a day. Two others were 

 taken shortly afterward, one on the 1st and one 

 on the 2d of May 1951. Then on September 11, 

 1953, a fourth was caught, 877 days after the 

 date of release. Hatchery releases are listed 

 in tables 4-12. 



The above release excluded, the best 

 indication is that the rate of travel of bluebacks 

 released in the spring from Leavenworth and 

 Winthrop averages 12 to 25 miles a day. A 

 spring release from Little White averaged less 

 than 2 miles a day . 



Catches of Marked Fish 



Leavenworth and Winthrop hatcheries 

 are approximately 350 and 420 miles above 

 Bonneville Dam; Little White hatchery is approx- 

 imately 20 miles above Bonneville. More marked 

 bluebacks were caught from fish released in the 

 spring than those released in the fall from 

 Leavenworth and Winthrop; more marked blue- 

 back were caught from a fall than from a spring 

 release from Little White . No bluebacks were 

 caught at Bonneville from 49, 286 marked 2's 

 released in October and November into the Met- 

 low River by Winthrop hatchery; 27 marked 2's 

 were caught from 42, 332 released in March 

 into the same river . Three bluebacks were 



26 



